It's a 2-gallon Marineland Eclipse. Unfortunately I do need his filter, because as a very busy college student the most I can keep up with is the bare minimum of water changes. I adapted the water bottle filter baffle tutorial to fit my filter so there is barely a current left to bother him. I'm going to try tying some netting around the intake to keep his fins from getting stuck.
I am certain it's not new growth, though. His fins are looking way too ragged for that, and there are actually holes which wouldn't make sense for that.
I went and picked up some aquarium salt from the store today, as well as all new decor that I am 100% certain will not damage him and some blood worms (I'm going to see if any variety in his diet helps). I'll do a 100% water change today and clean everything out before starting the salt treatment.

Okay I understand. Poor thing I hope he gets better. The AQ salt should help. Do you have IAL?

Okay I understand. Poor thing I hope he gets better. The AQ salt should help. Do you have IAL?

I don't know what IAL is, haha, so I guess not. What does it do?

Aaand update!
After a 100% water change, full tank cleaning, new plants, aquarium salt, conditioner, and a couple drops of stress coat, Gawain appears to be on the mend. The holes in his fins closed up overnight, and the tears already look shorter. Thank you all so much for your help and advice!

I'm sorry I was being lazy by putting IAL, lol. Indian Almond leaf. It is the best for keeping your bettas healthy and to aid in natural healing. You can find a lot of sellers online. I get mine from ebay. ;) Let me find a thread that fully explains how wonderful these leaves are. ;)

This is the seller I buy mine from. He has great info on his listing actually. I'm gonna cut and paste what he wrote. Here is the link as well. Ebay listing

Ketapang or Sea Almond or Indian Almond or Terminalia catappa leaves are known to most, if not all Asian breeders of blackwater tropical fishes, to be one of the best water conditioners to promote healing and breeding. They are known to have antibacteria and antifungal properties. Bettas are known to be induced to spawn by just putting a few of the leaves into their tank. Fish suffering finrot or injuries (such as spawning injuries) will definitely benefit from having the leaves in their quarantine tub. But they can be used for the usual aquariums too.

When soaked in water these leaves will leach a strong brown dye that is full of organic acids like humic acids and tannic acids. These may be useful for inhibiting many types of bacteria as well as to detoxify harmful heavy metals found in the aquarium.

When soaked in water these leaves will leach a strong brown dye that is full of organic acids like humic acids and tannic acids. These may be useful for inhibiting many types of bacteria as well as to detoxify harmful heavy metals found in the aquarium.

Strong brown dye? Wouldn't that murk up the water or something?
...Or even actually dye my fish? His fins are pretty white/transparent.

It turns the water light amber to dark amber depending on how many leaves you put into the water. The seller lists a recommended amount depending on tank size. The amber color is actually very comforting for the fish. This dye/coloring happens over time as the leave steeps. I have a marbled plakat and he is pretty light but nothing has changed with his color. So no worries it will not dye your fish, lol. )